Dimensionally heat-recoverable articles are well known and are used for enclosing many substrates, for the provision of environmental sealing, mechanical protection and/or electrical insulation for example. Depending on the use to which the articles are to be put, the material from which the articles are made is often required to have one or more of a variety of different properties. This `tailoring` of properties is often achieved by the incorporation of additives in a polymeric material. Examples of the types of additives that are used include antioxidants, reinforcing or non-reinforcing fillers, flame retardants, plasticisers, pigments, stabilisers and lubricants.